1. Field of the Invention
This invention relates to a new and improved fluid resistant, durable enclosure for a geophone electrically connected to a cable. In particular, this invention relates to a fluid resistant enclosure having a fluid tight interior adapted for use in the seismic industry as a fluid resistant, durable enclosure for enclosing a seismometer for detecting seismic waves produced by a seismic energy source in marshes, swamps and other damp and wet geographical locations.
2. Disclosure of the Prior Art
It is known in the prior art to use a fluid tight, high impact polycarbonate (LEXAN cases) to enclose or house a geophone which is electrically connected to a cable which passes through the case. Use of a knot anchored takeout to prevent withdrawal of the cable from the case and disconnection of the cable from the geophone is known and described in U.S. Pat. No. 3,119,978.
There are a number of other known fluid tight enclosures or fluid resistant enclosures for use with geophone and cable. Typical of the known devices are those described in U.S. Pat. Nos. 2,908,890, 3,445,809 and 3,993,859, the latter which has a common assignee with the present application.
The seismophone and cable assembly described in U.S. Pat. No. 2,908,890 utilizes a housing which functions as a protective case for the components which actually comprise the geophone. The protective case is formed integrally with an interconnecting cable to insure that seismophones and seismophone case will not be damaged by pulling on the interconnecting cable. A cap, which is mounted through a sealing ring to the housing of the protective case, functions both as the top to the seismophone housing and to the protective case.
U.S. Pat. No. 3,445,809 discloses a geophone housing and takeout. The housing is adapted to receive a geophone which is an integral component pre-assembled and adapted to be electrically connected to a cable. The geophone housing of U.S. Pat. No. 3,445,809 includes a rubber geophone takeout which is molded about and affixed to a cable carrying electrical conductors. The takeout terminates in a molded rubber cup having the frustro-conical surface, the interior of which encloses and directly engages the exterior of the geophone without anything therebetween. A top cooperates with the housing and the molded takeout, attached to the electrical cable, to form a fluid tight housing relying primarily on the integral relationship between the molded takeout and the cable and the seal formed between the exterior of the molded takeout and the top and housing.
U.S. Pat. No. 3,993,859 discloses a fluid tight enclosure for geophone and cable having a flexible header and stress ring. The flexible header is removably affixed to a cable. The stress ring is located within the flexible header and cooperates with an annular shaped ring member, which is integral with the flexible header, for forming a fluid tight seal between the annular shaped ring member and top of the geophone and between the housing, cable supports and the cable. The stress ring is capable of retaining a cable, having a knot anchored takeout therein, to prevent withdrawal of the cable through the flexible header while concurrently forming a fluid tight seal between the annular shaped ring member and housing.
The prior art cases have several disadvantages. One disadvantage is that, under continuous usage, the fluid tight seal between the plastic housing and top or housing segments may leak. Further, if the case is fabricated from a plastic material, the plastic material itself is subject to deterioration from sunlight and temperature extremes. Also, under certain conditions, the case may become cracked. Fluid could enter through the deteriorated or disrupted seals, case or cracks, to disable the geophone operation. In such event, the fluid would short out or otherwise affect the electrical connections between the electrical cable and geophone. The fluid tight enclosure for geophone and cable described in U.S. Pat. No. 3,993,859 provides a sealing means for keeping the fluid away from the terminals of the geophone which are electrically connected to the cable. However, in the event that the case is cracked or broken, the seal between the stress ring and annular sealing rings will effectively provide an interior seal to inhibit fluid from entering directly into the hollowed out central area of the flexible header. In the event that fluid did enter into the cavity of the housing, the fluid would enclose the geophone housing. Also, under very high pressure, fluid may travel within the interior of the cable, through the cable supports, and enter the hollowed out area of the header, thereby shorting the terminals of the geophone.